Conventionally, there is known the method of computing a user speed on the geocentric orthogonal coordinate system and its time offset rate by simultaneous speed equations. The simultaneous speed equations are constructed using a user position on the geocentric orthogonal coordinate system determined by simultaneous position equations, and the time offset. The differentiated value of the speed on the geocentric orthogonal coordinate system with respect to time is determined by solving the simultaneous speed equations. Each value required by the user is computed by obtaining the differentiated value of the speed on the geocentric orthogonal coordinate system with respect to time through transforming of the geocentric orthogonal coordinate system into the geocentric orthogonal coordinate system at the user position. For example, refer to Japanese patent No. 2963912.
Generally, in GPS (global positioning system) positioning, measurement of a position of a mobile unit is performed based on the results of received signals from a plurality of satellites. At this time, the radio propagation paths from the respective satellites to the mobile unit are different from each other, and a different error for each satellite may be included in the measured value (for example, pseudo distance) obtained based on the received signals from the respective satellites. For this reason, when performing GPS positioning, there are cases in which a weight is assigned for each satellite.
Conventionally, in many cases, the weighting factors used in the above-mentioned weighting are determined in accordance with the residual difference at the previous instant of the positioning computation, the difference in the elevation angle of each satellite, or the difference in the intensity of the signal received from each satellite. However, there is a problem that using the determined weighting factors is not appropriate for reflecting a different error for every satellite.